hard shells that allow reptiles to lay eggs on land

A) directional selection
B) sexual dimorphism
C) sympatric speciation
D) balanced polymorphism
E) coevolution
F) allopatric speciation
G) key innovation
H) adaptive radiation

Hard Shells

Rigid external coverings that provide protection to the bodies of certain animals, like mollusks and turtles.

Reptiles

A class of cold-blooded, air-breathing vertebrates characterized by their skin covered in scales or hard plates, laying eggs, and typically having a three-chambered heart.